Television receiving apparatus



Filed Aug. 22, 1935 rucuzaumm MEDPUE INVENTOR MAISON CAWEIN.

ATTORNEY mwzuomm Patented Aug. 15, 1939 TELEVISION RECEIVING APPARATUS Madison Cawein, Manhasset, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application August 22, 1935, Serial No. 37,294

13 Claims.

tials to the electrodes of suchtubes.

It is desirable that the application of operating potentials to the several electrodes of a cathode-ray tube be effected by a single switching operation. Such an arrangement is particularly desirable in connection with television re-,

ceiving apparatus consisting of ajplurality of component units which receive power from a single line, so that a minimum number of controls forv the apparatus will be needed. This arrangement, however, gives rise to certain problems, due to undesirable transient effects which tend to arise subsequent to the switching operation and before all the electrodes or component parts of the apparatus have reached their normal operating potentials or conditions. More particlularly, it is ordinarily necessary to employ a large timeconstant filter circuit in connection with the normally negatively biased main or video control grid of the cathode-ray tube, for isolation purposes; that is, in order to prevent hum and other undesirable power supply reactions from modulating the electron beam of the tube. Such a filter circuit introduces a time delay in the application of the negative bias to the control grid after the single switching operation necessary to initiate operation of the system. Also a delay in the application of the negative bias to the control electrode may be introduced by the video frequency input circuit which is coupled thereto.

Since the application of normal operating potentials to the tube electrodes is usually delayed until the cathode reaches normal operating temperature, and since positive potentials are ordinarily applied to the normally positively charged electrodes of the tube without further delay, the additional time delay, described above, in the application of negative bias to the main control grid may permit a momentary impingement of the electron beam in full intensity upon the fluorescent screen at the end of the tube, with the possible result of permanent damage to the tube and, in any event, of a light flash which is quite objectionable to the eye.

It is, therefore, an object of the present invention to provide an arrangement for preventing the impingement of the electron beam of a cathode-ray tube upon the screen thereof with sufficient intensity to produce undesirable effects, uponinitiation of the operation of the tube,

In accordance with the present invention, the aforementioned undesirable effects are prevented by the rovision of a time delay circuit or circuits in operative relation with one or more of the normally positively charged electrodes of the tube. In a preferred embodiment of the invention, the delay circuits, each comprising a resistance and a condenser, are connected in the operating potential supply leads of the second grid and first anode of the tube, which electrodes exert considerable control on the intensity of the beam. The elements of the time delay circuits for these two normally positively biased electrodes are proportioned to provide time delays therefor which are of the same order as the time delay in the application of negative biasing p0 tential on the main control grid, introduced by its isolating circuit as well as by the video cou-, pling circuit. The electron beam intensity is thus prevented, upon initial application of the operat: ing potentials to the control electrodes of the tube, from becoming momentarily sumciently great to have any of the described undesirable efiects.

For a better understanding of my invention, together with other and further objects thereof, reference is had to the following detailed description of a preferred embodiment of the invention, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

The single figure of the drawing is a circuit diagram, partly schematic, of a complete television receiving system embodying my invention.

Referring now to the drawing, the television system illustrated comprises a receiver, indicated schematically at 6, connected to an antenna and ground system I0H. The receiver 6 will be understood to include a sound-radio selecting, amplifying, detecting and reproducing unit, which may be of a conventional type, and a television selecting, amplifying and detecting unit, which may also be of any well-known type. The system includes also a picture frequency generator I and a line frequency-generator 8, connected for synchronization to the television unit of the receiver in the usual manner, and a cathode-ray tube H2, or similar scanning device, which is connected to the generators l and 8 and to the receiver 8 in a manner presently to be described.

Power supply means, indicated generally by the numeral 9, is provided for supplying operatand the electrodes of the cathode-ray tube I 2.

power transformer including a primary winding la and a plurality of secondary windings 2a2e. The primary winding is preferably adapted for connection to an alternating-current power line by a plug l3 through a control switch I4. The secondary winding 2a is connected to a suitable power supply unit 5, which will be understood to include conventional rectifying and filtering apparatus, for providing operating potentials to the receiver 6 and generators I and 8. Secondary windings 2b and 2c are connected, in the usual manner, to the cathode heating and plate circuits, respectively, of a mercury vapor or other gaseous rectifier 3, from which directcurrent potentials are applied across a voltage divider l5. In order to insure proper operation of the system, a time delay device 4, of any suitable well-known type, is preferably included in the rectifier circuit and energized from the secondary winding 2d. Operating current is supplied to the cathode heater |2a of the cathoderay tube by means of the secondary winding 2e. The voltage divider I5 is grounded at l8 and' serves to provide proper operating potentials for the several electrodes of'the tube l2.

The cathode-ray tube I2 comprises the usual envelope l9 containing a cathode 20, a main or video control grid 2|, a second grid 22, a first anode 23, a second anode 24 and the usual fluorescent screen 24a. Line frequency electrostatic deflecting or scanning plates 26 are disposed within the tube l2 and picture frequency electromagnetic deflecting or scanning coils 21 are disposed at opposite sides of the tube, producing a magnetic field for deflecting the beam. in a direction normal to the direction of deflection of the beam by the electrostatic field of the plates 26. The cathode is connected to ground through conductor25. Video frequencies are impressed on the main control grid 2| from the receiver 6 through conductor 28 and a coupling condenser 23. A negative biasing potential is applied to the control grid 2| through resistors 3| and 39 from a suitable point on the divider l5. Positive potentials are applied to "the second grid 22, the

first anode 23 and the second anode 24 by conductors 32, 33 and 34, respectively, which connect these electrodes to appropriate points on the divider IS.

The line frequency scanning voltages are supplied from the generator 8 to the scanning plates 26 through conductors 35 and suitable direct-current blocking condensers 36, the same biasing potential as is applied to the second anode 24 being supplied also to these plates through conductor 34 and resistors 31. Picture frequency scanning currents are supplied from the picture frequency generator'1 to the 00115 21 through conductors 38. I

The general operation of the system thus far described is conventional. Briefly, when the switch I4 is closed, operating potentials are s'upplied to the receiver 6 "and generators I and 8 through the medium. of the unit 5; operating cur rent for the heater |2a is supplied from the 'wind ing 2e, and operating potentials for the cathode and anodes of the tube I2 are supplied through the rectifier 3 and voltage divider l5. By virtue of the time delay action of thedevice 4, the application of high potentials to the'anode of the rectifier 3 is delayed until after the rectifier cathode is heated sufliciently to prevent damage to the tube, as well understood in the art. As a consequence of this action the application of po- The power supply means may comprise a main tentials to the electrodes of the cathode-ray tube I2 is delayed until its cathode has reachedits normal operating temperature. An electron beam is then emitted from the cathode and its intensity is modulated or controlled by the grid 2| in accordance with the video frequency supplied from the receiver 6. The second grid 22 serves to control the average intensity of the beam, while the first anode 23 co-operates with the second anode 24 to accelerate and focus the electron beam. The plates 26 and coils 2| serve to deflect the beam in proper synchronism, according to the frequencies supplied by the line frequency and picture frequency generators, so that the beam impinges upon and scans the fluorescent screen 24a to reproduce a received picture in thewell-known manner. 7, 7,

Referring now-to the circuit elements more directly involved in the present invention, it has been found necessary, in order to isolate the control grid 2| for the purpose of preventing modu-' lation of the beam by hum and other undesirable power supply reactions, to provide in the biasing connection to the power supply 'a filtering circuit of relatively large time constant. This filtering circuit comprising an isolating resistance 39 and a by-pass condenser 40 to the cathode, which is grounded as shown. The resistance 39 and condenser 40 are proportioned to provide a time constant sufliciently great to suppress the undesirable power supply reactions above mentioned.

The presence of. this filter circuit results in a certain delay in the application of the negative grid bias to the grid 2| upon closing the switch l4 and the operation of time delay device 4 to place the tube |2 in condition for picture reproduction. It will be noted also that, in the operation of the system, the condenser 29 and the resistance 3| of the video coupling circuit may delay the application of the grid bias to a certain extent.

With the arrangement so far described, it will be seen that, upon the closing of the switch H to initiate operation of the system, the heater I21; and the cathode 20 will be brought to operating temperature after a short interval and positive potentials will thereafter be applied simultaneously to all of the positive electrodes 22, 23 and 24. However, the application of the negative biasing potential to the grid 2| will be delayed for an appreciable interval as described above, Under these conditions the electron beam would momentarily impinge upon the fluorescent screen of the tube in full intensity, resulting in possible permanent damage to the tube or, in any event, in creating a light flash objectionable to the eye.

In order to compensate for the delay in application of the negative bias to the control grid and to eliminate the undesirable effects mentioned, there is provided a time delay circuitin connection with one or more of the normally positively charged electrodesof the tube. Pref-. erably, a time delay circuit is provided in connection with the second grid 22, which grid has a substantial effect upon the intensity of the beam. This time delay circuit comprises an isolating resistance 4| anda by-pass condenser 42 to the cathode. Further compensating delay circuits may be provided in connection with one or both of the other normally positively charged electrodes 23-and 24. For example, as shown, a time delay circuit for the electrode 23 comprises an isolating resistance 43 and a by-pass condenser 44 to the cathode.

The elements of each of the compensating delay circuits are so proportioned as to impart thereto a time constant which is of the same order as, and preferably greater than, the time constant of the filter circuit included in the biasing connection of the control grid 2|, and also preferably sufliciently large to take care of any additional delay occasioned by the resistance 3| and the condenser 29 of the video coupling circuit. By virtue of this delay in the application of the positive potentials to one or more electrodes of the tube l2, the electron beam is prevented from reaching full or abnormal intensity during the time immediately after the switching operation and the operation of the time delay device 4 to initiate operation of the. system, and before the negative potential applied to the control grid. builds up to its normal value, thereby obviating the undesirable results discussed above.

While I have described what I at present consider the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from my invention, and I, therefore, aim in theappended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

- What is claimed is:

1. An electric circuit arrangement for controlling an electron beam of a cathode-ray tube and for preventing said beam from becoming mo- 1 mentarily sufficiently intense to have undesirable effects by reason of the delayed application of a negative bias potential to a control electrode of said tube, comprising means including a single manual control means for applying a negative bias potential to said control electrode and a positive bias potential to a second control electrode, means tending to delay the application of said negative bias to said first control electrode, and means for automatically delaying the application of a positive potential to the said second control electrode for a period at least as great as the delay in'said application or negative potential, to limit thereby the intensity of the beam until said negative potential reaches its normal value.

2. An electric circuit arrangement for controlling an electron beam of a cathode-ray tube and for preventing said beam from becoming momentarily sufiiciently great to have undesirable efiects by reason of the delayed application of a negative bias potential to a control electrode of said tube, comprising individual circuits for applying a negative bias potential to said control electrode and a positive bias potential to a second control electrode, a single manual means for controlling the energization of said circuits, means tending to delay the application of said negative bias potential to said first control electrode, and a time delay circuit connected in circuit with said positive biasing circuit .for antomatically delaying the application of positive potential to said second control electrode for a period at least as great as said delay of application of negative potential, to limit thereby the intensity of the beam until said negative potential reaches its normal value.

3. In a television receiving system, a cathoderay tube having a plurality of electrodes including a normally negatively biased first electrode and a normally positively biased second electrode,

a single manual control means for controlling the application of operating potentials to said electrodes, means delaying the application of negative potential to said-first electrode, and means automatically delaying the application of positive potential to said second electrode for a period at least as great as said delay of the application of negative potential.

4. In a television receiving system, a cathoderay tube having a plurality of electrodes including a normally negatively biased first control grid and'a plurality of normally positively biased electrodes, a single means for applying the operating potentials to said electrodes, means delaying the application of negative potential to said control grid, and means automatically delaying the application of normal positive potential to one or more of said normally positively biased electrodes for a period greater. than the delay of the application of normal negative potential.

5. In a television receiving system, a cathoderay tube having a plurality of electrodes including a normally negatively biased control grid and a normally positively biased electrode, a single manual means for controlling the application of operating potentials to said electrodes, a time delay circuit including a resistance and a condenser connected in circuit with said control grid, and a second time delay circuit including a resistance and a condenser connected in circuit with said normally. positively biased electrode and having a time constant at least as great as the time constant of the first said delay circuit.

6. In a television system, a cathode-ray tube having a plurality of electrodes including a control grid normally negatively biased relative to said cathode and a normally positively biased electrode, a power source, means for effecting the application ofoperating potentials to said electrodes including a voltage divider, switching means for controlling the energization of said divider from said source and connections from said electrodes to appropriate points on said divider, means delaying application of negative potential to said control grid including an isolating resistance and a by-pass condenser in cincuit therewith and means delayingthe application of positive potential to said normally positively biased electrode including an isolating resistance and a by-pass condenser in circuit therewith, the electrical values of the last said delay means being proportioned to provide. a time constant therefor at least as great as the time constant of the first said delay means.

7. In combination, a cathode-ray tube including a cathode, a control gridand a plurality of anodes, a power source, means including a single switching means for controlling the application of potentials from said source tosaid electrodes and establishing, relative to said cathode, a negative biasing potential on said control grid and positive operating potentials on said anodes, electrical means delaying the establishment of said negative bias on said grid and compensating electrical means for delaying, for a period at least as great as the period of the first said delay, the establishment of a positive operating potential on at least one of said anodes.

8. In combination, a cathode-ray tube including a cathode, a control grid and a plurality of anodes, a power source, means including a single switching means for controling the application of potentials from said source to said electrodes and establishing, relative to said cathode, a negative biasing potential on said control grid and positive operating potentials on said anodes, electrical means delaying the establishment of said negative bias on said grid and compensating the establishment of a positive operating potential on at least one of said anodes, the first said .5 electrical means comprising a resistance and a condenser having a predetermined time constant and the second said electrical means comprising a resistance and condenser having a time constant' at least as great as the first said time con- 110 stant.

9. In combination, an electrical apparatus, a power source,-a distributing network including a plurality of separate circuits for individually supplyinga plurality of separate unidirectional potentials for operating said apparatus, means including a single manual means for simultaneously energizing said plurality of circuits from said source, each of said circuits including a resistor and a condenser havinga predetermined time 20 constant of such magnitude that said circuits and said means cooperate to develop maximum unidirectional potentials for operating said apparatus at diiferent times in each of said circuits.

10. In combination, a cathode-ray tube having 25 a cathode heater and a plurality of electrodes, a

potential divider, means, including main switching means and a source of power for supplying alternating current to said heater and unidirectional potential across said potential divider, a

30 plurality of connections v f or applying positive and negative potentials from said potential divider to said electrodes, means delaying the application of unidirectional potential across said potential divider for a predetermined period after the clos- 35 ing of said main switching means, isolating means in the connection for applying negative potential from said potential divider to one of said electrodes providing a delay in the application of said negative potential, and means in the 40 connection for applying positive potential to at least one other 01' said electrodes for automatically delaying the application of said positive potential for a period of the order of the period of said delay in the application of said negative 5 potential,

- 11. The method of controlling the electron beam of a cathode-ray tube having a first control electrode and a second control electrode and including potential delaying means in circuit with said first control electrode, and preventingsaid beam from becoming momentarily sufllciently intense to have undesirable effects by reason of the delayed application of a negative bias to said first control electrode which consists in applying a negative bias to said first control electrode and a positive bias to said-second control electrode, and delaying the application of said positive bias to said second control electrode for a period greater than the delay of application of negative potential, thereby to limit the intensity of said .beam until said negative potential has reached its normal value.

12. The method oi applying positive and negative potentials to electrodes of a cathode-ray tube, which comprises simultaneously initiating the application of said potentials, delaying the application of said negative potential for a predetermined period subsequent to said initiation and automatically delaying the application of said positive potential for a predetermined period at least as great as the period of the delay of application of negative potential.

13. In combination, a tube provided with a screen and with means for developing a ray of ,mon with respect to said third-named and said fourth-named means for supplying the same with operating power, said third-named means being characterized by the fact that upon application of the operating power it has a time constant of operation substantially less than the time-constant of operationv of said fourth-named means.

MADISON CAWEIN. 

